docs: def count_variants(graph):
      """Count how many of each type of variant a graph has.
  
      :param pybel.BELGraph graph: A BEL graph
      :rtype: Counter
      """
      return Counter(
          variant_data[KIND]
          for data in graph
          if has_variant(graph, data)
          for variant_data in data[VARIANTS]
      )